Backlight assembly and liquid crystal display having the same

ABSTRACT

A backlight assembly and an LCD having the same are disclosed to prevent wrinklings of optical sheets due to close contact of optical sheets or prism sheets. The backlight assembly includes multiple optical sheets disposed between a light guiding plate and a display unit, for the diffusion of light, collection of light and securing of horizontal viewing angle. The front surface or the rear surface of each of the optical sheets each has an embossing structure or a matte structure to decrease a contact area between the multiple optical sheets and to minimize frictions.

CROSS REFERENCE

This application is a continuation application of Applicant's U.S.patent application Ser. No. 10/068,918 filed on Feb. 11, 2002 now U.S.Pat. No. 6,769,782.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD), andmore particularly, to a backlight assembly and LCD having the samecapable of preventing optical sheets from wrinkling due to closestacking of optical sheets or prism sheets employed in the backlightassembly.

2. Description of the Related Art

Generally, LCDs are the representative flat panel display. In order todisplay an image in these LCDs, an electric power is applied to liquidcrystal having a specific molecular configuration to thereby vary themolecular arrangement of liquid crystal. The molecular variations ofliquid crystal change optical properties such as birefringence, rotarypolarization, dichroism and light scattering. The LCDs converts theoptical property changes into the variations in the visual properties,thereby displaying a desired image.

LCDs are generally classified into two types according to liquid crystalused: a twisted nematic (TN) type; and a super-twisted nematic (STN)type. These LCDs are also classified into an active matrix display typeusing switching devices and TN liquid crystal, and a passive matrixdisplay type using STN liquid crystal according to a difference in thedriving way.

The two typed LCDs have apparent difference. The active matrix typedisplay is employed in TFT-LCDs utilizing thin film transistors (TFT) asswitching element. The passive matrix display does not utilize TFT asswitching element. In other words, the passive matrix display does notneed complicated circuits such as TFTs.

LCDs are passive device that does not emit light by itself. Thus, LCDsneed a backlight assembly as light source to display images. Thisbacklight assembly is established at the rear surface of the LCD panel.

Recently, in order to secure the competitiveness of LCD products, LCDsare being developed in a slimmer and lighter structure. Especially,considering that the LCDs are mainly used for portable computers, thepresent LCDs deal with lightness more significantly.

In these LCDs, present interests are especially focused on roles andfunctions of the backlight assembly. This is because size and lightefficiency of LCDs become different and mechanical and opticalproperties are affected depending on the LCD structure to a considerabledegree.

There is disclosed a structure of a general backlight assembly used inthese LCDs in U.S. Pat. No. 5,467,208.

FIG. 1 is a simplified exploded perspective view of a conventional LCDhaving the backlight assembly, and FIGS. 2 and 3 are simplifiedsectional views of the backlight assembly of FIG. 1.

Referring to FIGS. 1 and 2, a backlight assembly includes a lamp 12 foremitting a light, a light guiding plate 20 for guiding the light emittedfrom the lamp 12, and a lamp cover 14 established at one side of thelight guiding plate 20, for surrounding the lamp 12.

As the lamp 12, a cold cathode lamp is mainly used. Light generated fromthe lamp 12 is incident through a side wall of the light guiding plate20. Inner surface of the lamp cover 14 is made of a reflector plate. Thelight guiding plate 20 reflects light generated from the lamp 12,thereby enhancing a light efficiency.

The light guiding plate 20 guides the light generated from the lamp 12to proceed toward an LCD panel 15 mounted thereon. The light guidingplate 20 includes various patterns such as a fine dot pattern (notshown) formed on the rear surface thereof to convert a light proceedingdirection toward the LCD panel 15.

A reflector plate 22 is disposed beneath the light guiding plate 20 anda diffusion sheet 32, a first prism sheet 34, a second prism sheet 36and a protective film 38 are placed in such an order on the lightguiding plate 20.

The reflector plate 22 reflects light beams that are not reflected bythe printed patterns of the light guiding plate 20 and leak, toward thelight guiding plate 20, thereby reducing loss of incident light to theLCD panel 15 and simultaneously enhancing the uniformity of light beamspassing through the light guiding plate 20 upward.

The diffusion sheet 32 is placed between the light guiding plate 20 andthe first prism sheet 34 and disperses the light incident from the lightguiding plate 20, to thereby prevent a partial concentration of lightbeams. A plurality of beads 32 a and 32 b are formed on the frontsurface and the rear surface of the diffusion sheet 32, and they makeuniform the light flux distribution of light beams reflected from thereflector plate 22.

The first prism sheet 34 and the second prism sheet 36 are stacked inthe named order on the diffusion sheet 32 and they each have a pluralityof triangle prisms at the front surface thereof. The first prism sheet34 and the second prism sheet 36 collect light beams diffused by thediffusion sheet 32 toward a first and second direction normal to a planeparallel to the LCD panel 40 in order to make a viewing angle narrow,thereby enhancing the brightness at the front side.

The protective film 38 is placed between the second prism sheet 36 andthe LCD panel 40 to protect the front surface of the second prism sheet36. The protective film 38 has a plurality of acryl beads 38 a formed atthe front surface thereof, to prevent moiré phenomenon and rainbowphenomenon. Thus, the light beams generated from the lamp 20 and thenpassing through multiple optical sheets show images formed by the LCDpanel 40.

Meanwhile, when the horizontal viewing angle is important, there iswidely used a backlight assembly structure utilizing only either one ofthe first prism sheet or the second prism sheet having a lightcollection characteristic and for enhancing the luminance at the frontside. In this case, a reflection polarization film is used, whichimproves a luminance lowering per viewing angles due to the lack of oneprism sheet, increases the luminance of the light through the entiresurface of the prism sheet and enhances the luminance characteristicsevery viewing angles.

FIG. 3 shows an example of a backlight assembly having only one prismsheet and a reflection polarization film for improving the brightnesscharacteristic from every viewing angle is also used.

As shown in FIG. 3, a reflection polarization film 39 is placed betweenthe first prism sheet 34 and the protective film 38. The reflectionpolarization film 39 has smooth front surface in contact with theprotective film 38 and smooth rear surface in contact with the firstprism sheet 34.

However, the aforementioned conventional backlight assemblies have thefollowing drawbacks. First, since the prisms formed at the front surfaceof the prism sheet have a shape of ridge, optical sheets wrinkle due toclose stacking of another prism sheet or the reflection polarizationfilm.

Second, when a single prism sheet and the reflection polarization filmare employed, a contact area is widened between the reflectionpolarization film and the underlying prism sheet and between thereflection polarization film and the overlying protective film,increasing a friction coefficient. As a result, curl occurs betweenoptical sheets.

Third, since the optical sheets are of compound resin, electrostaticcurrent is easily generated. The electrostatic current allows theoptical sheets to be closely attached to each other, however, creatingwrinkles between optical sheets.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide abacklight assembly that can prevent optical sheets and/or prism sheetemployed in the backlight assembly from wrinkling due to close contactbetween the sheets.

It is another object of the present invention to provide an LCD that canprevent optical sheets and/or prism sheet employed in the backlightassembly from wrinkling due to close contact between the sheets.

To accomplish the above objects, a backlight assembly comprises a lightgenerating part for generating a light, a light guiding part for guidingthe generated light to a display unit displaying an image, and a lightcontrol part disposed between the light guiding plate and the displayunit for enhancing a brightness of the light passing through the lightguiding part. Here, the light control part has a front surface facingthe display unit and a rear surface facing the light guiding part, atleast one of the front surface and the rear surface of the light controlpart being not flat.

According to another aspect of the present invention, an LCD comprises adisplay unit having an LCD panel for displaying an image using aprovided light, and a backlight assembly comprising a light generatingpart for generating a light, a light guiding part for guiding thegenerated light to a display unit displaying an image, and a lightcontrol part disposed between the light guiding plate and the displayunit for enhancing a brightness of the light passing through the lightguiding part. Here, the light control part has a front surface facingthe display unit and a rear surface facing the light guiding part, atleast one of the front surface and the rear surface of the light controlpart being not flat.

Here, the light control part is a reflection polarization film forenhancing the brightness of the light passing through the light guidingpart. The reflection polarization film has a front surface establishedclosely in direct contact with the display unit and having a mat shape,and a rear surface having an embossing shape.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and other advantages of the present invention willbecome more apparent by describing in detail the preferred embodimentsthereof with reference to the accompanying drawings.

FIG. 1 is a simplified exploded perspective view of an LCD having abacklight assembly in accordance with the conventional art.

FIG. 2 is a simplified schematic view of one example of optical sheetsin the backlight assembly of FIG. 1.

FIG. 3 is a simplified schematic view of another example of opticalsheets in the backlight assembly of FIG. 1.

FIG. 4 is a simplified exploded perspective view of an LCD having abacklight assembly in accordance with a preferred embodiment of thepresent invention.

FIG. 5 through FIG. 9 are schematic views showing various structures ofoptical sheets in the backlight assembly of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein.

FIG. 4 is a simplified exploded perspective view of an LCD having abacklight assembly in accordance with a preferred embodiment of thepresent invention. FIG. 4 shows an embodiment in which a single prismsheet and a reflection polarization film are employed. It is evident,however, the present invention embraces such modifications andvariations in which two prism sheets are used along with the reflectionpolarization film as described later.

Referring to FIG. 4, a backlight assembly in accordance with the presentinvention has a lamp unit 100 and a light guiding unit 300. The lampunit 100 includes a lamp 102 for emitting a light and a lamp cover 104surrounding the lamp 102 to protect the lamp 102 and reflecting thelight generated from the lamp 102 toward the light guiding unit 300, tothereby enhance a light efficiency. As the lamp 102, a cold cathode lampis mainly used.

The light guiding unit 300 includes a light guiding plate 202 forguiding the light emitted from the lamp 102. A reflector plate 204 isdisposed beneath the light guiding plate 202. A diffusion sheet 310, afirst prism sheet 320, a first reflection polarization film 330 and aprotective film 340 are placed in the named order on the light guidingplate 202.

On the protective film 340, there is disposed an LCD panel 400 fordisplaying an image in response to the light that is guided by the lightguiding plate 202 and provided through a plurality of optical sheets.

The lamp 102 and the lamp cover 104 are disposed adjacent to one sidewall of the light guiding plate 202. The light guiding plate 202 guidesthe light generated from the lamp 102 such that the light proceeds tothe LCD panel 400 disposed over the light guiding plate 202. On the rearsurface of the light guiding plate 202, there are formed variouspatterns such as a fine dot pattern (not shown in the drawings) so as toconvert the light proceeding direction provided from the lamp 102 towardthe LCD panel 400.

The reflector plate 204 reflects the light that is not reflected towardthe LCD panel 400 and leaks, toward the light guiding plate 202. Thus,loss of input light to the LCD panel 400 is minimized. At the same time,it enhances uniformity of light passing through the light guiding plate202.

The diffusion sheet 310 disposed between the light guiding plate 202 andthe first prism sheet 320 disperses the light that is incident to thelight guiding plate 202, thereby preventing partial concentration of thelight. Although not shown in FIG. 4, a plurality of beads 312 and 314are formed at the front and rear surface of the diffusion sheet 310,thereby making uniform a light flux distribution of the light reflectedfrom the reflector plate 204.

A plurality of triangle prisms are formed at the front surface of thefirst prism sheet 320 disposed on the diffusion sheet 310. The fistprism sheet collects light beams diffused by the diffusion sheet 310toward a specific direction normal to a plane parallel to the LCD panel400 in order to make a viewing angle narrow and thereby enhance thebrightness at the front side.

The first reflection polarization film 330 and the protective film 340are placed between the first prism sheet 320 and the LCD panel 400.

The first reflection polarization film 330 increases the brightness ofthe light collected by the first prism sheet 320 uniformly in order toimprove the brightness every horizontal viewing angles of the LCD panel400.

The protective film 340 protects the surfaces of the optical sheetsdisposed below the protective film 340. Also, the protective film 340has a plurality of acryl beads (not shown in FIG. 4) formed at the frontsurface, thereby preventing occurrences of moiré phenomenon and rainbowphenomenon that may be caused by the first prism sheet 320. Thus, thelight beams that are generated from the lamp 102 and then pass throughmultiple optical sheets show images formed by the LCD panel 400.Meanwhile, the front surface and the rear surface of the reflectionpolarization film 340 can be made to have a mat shape and an embossingshape, respectively. They will be fully described with reference to thefollowing drawings.

FIG. 5 through FIG. 9 show various structures of the backlight assemblyprovided in FIG. 4.

Referring to FIG. 5, the diffusion sheet 310, the first prism sheet 320,the first reflection polarization film 330 and the protective film 340are stacked in the named order on the light guiding plate 202. Theplurality of beads 312 and 314 are formed at the front and rear surfacesof the diffusion sheet 310 so as to uniformly distribute light flux inthe light reflected from the reflector plate 204.

Also, the front surface of the protective film 340 has a matte structureto prevent moiré phenomenon by the first prism sheet. The firstreflection polarization film 330 has the front surface and the rearsurface each having an irregular surface of an embossing structure.

As the front surface and the rear surface of the first reflectionpolarization film 330 are made to have the embossing structure, acontact area decreases to a remarkable degree between the front surfaceof the first reflection polarization film 330 and the rear surface ofthe protective film 340 and a contact area between the rear surface ofthe first reflection polarization film 330 and the front surface of thefirst prism sheet 320.

Accordingly, friction occurring between the front surface of the firstreflection polarization film 330 and the rear surface of the protectivefilm 340 and friction occurring between the rear surface of the firstreflection polarization film 330 and the front surface of the firstprism sheet 320 decrease to a remarkable degree. This prevents thewrinkling of the optical sheets disposed between the light guiding plate202 and the LCD panel 400.

FIG. 6 shows a backlight assembly having a reflection polarization film331 (hereinafter referred to as “second reflection polarization film”)that is different than the first reflection polarization film 330 shownin FIG. 5.

The second reflection polarization film 331 shown in FIG. 6 is madeintegrally with the LCD panel 400. At this time, the protective film 340is disposed between the second reflection polarization film 331 and thefirst prism sheet 320.

Thus, as the second reflection polarization film 331 is made integrallywith the LCD panel 400, the rear surface of the second reflectionpolarization film 330 has an embossing structure. As a result, itprevents the curl of the optical sheets due to the close contact betweenthe protective film 340 and the second reflection polarization film 331.

In the meanwhile, the protective film 340 used for protecting thesurfaces of the optical sheets and preventing moiré phenomenon andrainbow phenomenon can be removed when the first reflection polarizationfilm 330 of FIG. 5 is made to have the same structure than that of areflection polarization film (hereinafter referred to as “thirdreflection polarization film”) shown in FIG. 7.

In other words, referring to FIG. 7, between the light guiding plate 202and the LCD panel 400, there are disposed the diffusion sheet 310, thefirst prism sheet 320 and a third reflection polarization film 332.Likewise, a plurality of beads 312 and 314 are formed at the front andrear surfaces of the diffusion sheet 310 in order to uniformlydistribute the light flux of the light reflected from the reflectorplate 204.

The rear surface of the third reflection polarization film 332 is formedto have an embossing structure in order to prevent a close contact withthe underlying first prism sheet, and the front surface of the thirdreflection polarization film 332 is formed to have a matte structure.Thus, the matte structure of the front surface of the third reflectionpolarization film prevents the moiré phenomenon and rainbow phenomenon.

Unlike the close contact between the reflection polarization film andthe remaining optical sheets, the optical sheets in the backlightassembly may wrinkle due to the close contact between the prism sheets.Especially, when at least two prism sheets are used or theaforementioned diffusion sheet is not used, this curl may occurfrequently. A surface structure of a prism sheet capable of preventingsuch a curl is shown in FIG. 8 and FIG. 9. The surface structures of theprism sheets provided in FIG. 8 and FIG. 9 can be equally applied to thefirst prism sheet shown in FIG. 5 through FIG. 7.

Referring to FIG. 8, between the light guiding plate 202 and the LCDpanel 400, there are disposed a second prism sheet 321 modified from thefirst prism sheet 320 shown in FIG. 7 and the third reflectionpolarization film 332. In other words, the second prism sheet 321 ismounted on the front surface of the light guiding plate 202 such that itdirectly, closely contacts the front surface of the light guiding plate202.

The rear surface of the third reflection polarization film 332 is formedto have an embossing structure 332 b in order to prevent a close contactwith the front surface of the second prism sheet 321. And the frontsurface of the third reflection polarization film 332 is formed to havea matte structure 332 a in order to prevent the moiré phenomenon andrainbow phenomenon. Likewise, the rear surface of the second prism sheet321 has an embossing structure 321 a in order to reduce the contact areawith the light guiding plate 202. Thus, since the contact area betweenthe second prism sheet 321 and the light guiding plate 202 decrease to aconsiderable degree by closely contacting the second prism sheet 321directly with the front surface of the light guiding plate 202 withoutusing the diffusion sheet, a curl between them can be prevented.

FIG. 9 shows a backlight assembly that uses two prism sheets andprotective film, but not a diffusion sheet.

Referring to FIG. 9, between the light guiding plate 202 and the LCDpanel 400, there are disposed the second prism sheet 321, a third prismsheet 350, a fourth reflection polarization film 334 and the protectivefilm 340.

The rear surface of the second prism sheet 321 a has an embossingstructure 321 a in order to decrease the area contacting the lightguiding plate 202. The rear surface of the third prism sheet 350 has anembossing structure 350 a in order to decrease the area contacting theprisms formed at the front surface of the second prism sheet 321.

Like the first reflection polarization film 340, the front and rearsurfaces of the fourth reflection polarization film 334 have anembossing structure in order to decrease the areas contacting theprotective film 340 and the third prism sheet 350, respectively. Also,each of the protective film disposed between the fourth reflectionpolarization film 334 and the LCD panel 400 has a front surface of amatte structure 341 in order to prevent moiré phenomenon and rainbowphenomenon due to the second and third prism sheets 321 and 350.

Like the third reflection polarization film 332 shown in FIG. 7 and FIG.8, respectively, when the fourth reflection polarization film 334 has arear surface of the embossing structure and a front surface of the mattestructure, the protective film 340 of FIG. 9 can be omitted.

As described above, the reflection polarization film in the backlightassembly and the LCD of the present invention is made to have the frontsurface of the embossing structure and the rear surface of the mattestructure. Also, the prism sheet is formed to have the rear surface ofthe embossing structure. As a result, a contact area between theplurality of optical sheets disposed between the light guiding plate andthe LCD panel decreases and the friction also decreases, therebypreventing curl of the optical sheets due to the close contact of theoptical sheets.

In addition, when the front surface of the reflection polarization filmhas a matte structure, the reflection polarization film prevents moiréphenomenon and rainbow phenomenon caused by the prism sheet, and therebythe protective film can be omitted from the backlight assembly.Moreover, when the rear surface of the prism sheet has an embossingstructure, the prism sheet can prevent curl of the prism sheet generatedby closely contacting the prism sheet directly with the light guidingplate although the diffusion sheet is omitted.

This invention has been described above with reference to theaforementioned embodiments. It is evident, however, that manyalternative modifications and variations will be apparent to thosehaving skills in the art in light of the foregoing description.Accordingly, the present invention embraces all such alternativemodifications and variations as fall within the spirit and scope of theappended claims.

1. A backlight assembly, comprising: a light generator that generates alight; an optical sheet disposed on the light generator so as to diffusethe light from the light generator and provide the diffused light to adisplay unit; and a reflection polarization film disposed between theoptical sheet and the display unit so as to enhance brightness of thelight provided to the display unit from the light generator through theoptical sheet, wherein the reflection polarization film has a frontsurface facing the display unit and a rear surface facing the opticalsheet, at least one of the front surface and the rear surface of thereflection polarization film being non-flat.
 2. The backlight assemblyof claim 1, wherein the front surface of the reflection polarizationfilm is in close and direct contact with the display unit.
 3. Thebacklight assembly of claim 2, wherein at least one of the front surfaceand the rear surface of the reflection polarization film have a mattestructure or an embossing structure.
 4. The backlight assembly of claim3, wherein the front surface of the reflection polarization film has thematte structure and the rear surface of the reflection polarization filmhas the embossing structure.
 5. The backlight assembly of claim 1,wherein the optical sheet comprises at least one prism film disposedbetween the reflection polarization film and the light generator so asto enhance the efficiency of collecting the light from the lightgenerator.
 6. The backlight assembly of claim 5, wherein the prism filmhas a facing surface facing the reflection polarization film and thefacing surface has a matte structure or an embossing structure.
 7. Thebacklight assembly of claim 1, further comprising a protective sheetdisposed between the reflection polarization film and the display unitso as to prevent interference of the light.
 8. The backlight assembly ofclaim 7, wherein the front surface and the rear surface of thereflection polarization film have the embossing structure.
 9. A liquidcrystal display device, comprising: a display unit having a liquidcrystal display panel that displays an image; and a backlight assembly,comprising: a light generator that generates a light; an optical sheetdisposed on the light generator so as to diffuse the light from thelight generator and provide the diffused light to a display unit; and areflection polarization film disposed between the optical sheet and thedisplay unit so as to enhance brightness of the light provided to thedisplay unit from the light generator through the optical sheet, whereinthe reflection polarization film has a front surface facing the displayunit and a rear surface facing the optical sheet, at least one of thefront surface and the rear surface of the reflection polarization filmbeing not flat.
 10. The liquid crystal display device of claim 9,wherein the front surface of the reflection polarization film is inclose and direct contact with the display unit.
 11. The liquid crystaldisplay device of claim 10, wherein the front surface and the rearsurface of the reflection polarization film have a matte structure or anembossing structure.
 12. The liquid crystal display device of claim 10,wherein the front surface of the reflection polarization film has thematte structure and the rear surface of the reflection polarization filmhas the embossing structure.
 13. The liquid crystal display device ofclaim 9, wherein the optical sheet comprises at least one prism filmdisposed between the reflection polarization film and the lightgenerator, the prism film enhancing the efficiency of collecting thelight generated from the light generator.
 14. The liquid crystal displaydevice of claim 13, wherein the prism film has a facing surface facingthe reflection polarization film and the facing surface has a mattestructure or an embossing structure.
 15. The liquid crystal displaydevice of claim 9, further comprising a protective sheet disposedbetween the reflection polarization film and the display unit so as toprevent interference of the light.
 16. The liquid crystal display deviceof claim 15, wherein the front surface and the rear surface of thereflection polarization film have an embossing structure.